Method of and device for automatically ascertaining the heating value of gases with reference to a certain normal condition



March 30, 1965 G. NIEDERGESASS 3,175,397

METHOD OF AND DEVICE FOR AUTOMATICALLY ASCERTAINING THE HEATING VALUE OFGASES WITH REFERENCE I TO A CERTAIN NORMAL CONDITION Filed Nov. 15, 1961m ll hsi i q gt U k Jana/ .107123 United States Patent Office PatentedMar. 30, 1965 8 Claims. iii. 73-190 The present invention relates to amethod of and device for automatically ascertaining the heating value ofgases with regard to a certain normal condition. More specifically, thepresent invention concerns the automatic and continuous ascertainment ofthe heating value or combustion heat of combustible gases whileemploying for instance air or water as heat carrier, the ascertainedheating value being referred to a comparable normal condition. Byheating value is meant the lower heating value, whereas the upperheating value is designated as combustion heat.

The heretofore known automatic calorimeters for measuring the heatingvalue with air as heat carrier have certain drawbacks with regard tomaintaining the volume relationship of gas to air precisely constant andalso with regard to the condition of these two substances so that aprecise measurement could not be obtained.

Devices are known in the art according to which gas and air are chargedwith an undefined content of moisture, and there are also known deviceswith which the employed gas and air are saturated with steam without,however, correspondingly considering the steam content which varies withthe temperature and which with the air water mixture changes thespecific heat.

A well known calorimeter which does not measure the heating value butthe combustion heat operates with mechanically driven volume meters formaintaining constant the relationship of gas to air and which humidifiesboth substances with steam up to the saturation point. This knowndevice, however, lacks means for considering or taking into account thefact that with diiferent temperatures a different specific heat of thesteam air mixture is encountered so that the said device can furnish aprecise measurement of the combustion heat per Nm. (nonnal cubic meters;definition see below at Formula 5) gas at a certain referencetemperature only. Deviation from this reference temperature must bynecessity cause measuring errors unless a correction is effected byhand.

According to another heretofore known calorimeter. neither ahumidification of gas and air up to the saturation point is effected nora computation of the heating value to a normal condition. The said knowndevice is equipped with means to compensate for variations in thedensity of the gas, this compensation being effected by the buoyancyvarying in conformity with the density variations of the gas in avertical pipe in connection with a choke mechanism. This arrangement,however, has the drawback that it easily results in faulty measurementsin view of the fact that the low gas pressures in front of the mainnozzle to the burner and the compensation nozzle to the vertical orstand pipe are easily affected by pressure variations in the room or bydraft air.

Furthermore, a method has become known Which is intended to overcome thelast mentioned drawbacks. This method, however, does likewise not takeinto consideration the influence which the steam content of the air,which varies at varying temperatures, exerts upon the measured valuewhich consideration, however, is indispensable for a precise measurementof the heating value. In addition thereto, with this device due to theprevailing differences in the temperature between air entrance andexhaust air mixture exit and the lower air admixture inherent thereto,the steam produced by the combustion of hydrogen in the combustible gasexerts a non-negligible influence upon the measured value.

It is, therefore, an object of the present invention to provide a devicefor and method of automatically ascertaining the heating value of gasesreferred to a certain normal condition, which will overcome the abovementioned drawbacks.

It is another object of this invention to provide a device for andmethod of automatically ascertaining the heating value of gases referredto a certain normal condition, which will make it possible precisely tomaintain constant the ratio or volume of gas to air and also will takeinto consideration the steam contained in the gas or air at thesaturation point thereof.

These and other objects and advantages of the invention will appear moreclearly from the following specification in connection with theaccompanying drawing diagrammatically illustrating a device according tothe present invention for carrying out the method according to thepresent invention.

More specifically, according to the present invention gas and air areprior to their entry into the combustion and mixing chamber insteam-saturated condition and at a corresponding pressure higher thanatmospheric pressure separately fed into known pressure control deviceswhich control the pressure of gas and air with regard to pressure valuesproportional to their specific weights. Pressure control devices of thetype involved are described for instance in the German periodicalGaswiirme vol. 5 (1956), pages to 110. To this end, branch currents ofsaid two substances gas and air are branched off from the pressurecontrols and are expanded to atmospheric pressure or to a higherconstant pressure. These branch currents are separately conducted to theentrance of two centrifugal blowers operating at the same orproportionally the same speeds. Such centrifugal blowers are known forinstance in connection with the dynamic measuring of specific weights.The said two separate currents are then in said centrifugal blowerscompressed to pressures proportional to their specific weights andhigher than atmospheric pressure. Centrifugal blowers of the typeinvolved are described for instance in the German periodical Das GasundWasserfach vol. 97 (1956), pages 461 to 465. The compression is effectedin conformity with the formula In this formula 1 stands for pressure, cis a blower constant or blower factor, and 7 stands for the specificweight in grams per cubic centimeters.

The outlet pressures of the blowers, when conveyed as control pressuresto pressure governors corresponding to the measuring devices, will withsaid pressure governors bring about control pressures of the same orproportional magnitude which as pressures in front of restrictors ormetering orifices or calibrated nozzles maintain an always uniform flowratio of gas and air. The flow through a nozzle or restrictor, as iswell known, can be expressed by the formula:

In this formula V is the quantity of flow in cubic centimeters persecond; F represents the opening cross section of the nozzle orrestrictor in square centimeters; a is a flow constant which takes intoconsideration the friction and the constriction of the gas jet; 6 is theexpansion factor considering the influence of the pressure drop atwritten as:

V 62 X x/ 1/ With h=p:c 'y (see Formula 1) there will be obtained Thismeans that a constant flow is obtained as long as the blower constantremains constant. The blower constant 0 can, however, change only inview of variations in the speed in which instance the blower constant ofboth blowers would vary at the same ratio because the said two blowersrotate at the same or at proportionally the same speeds. While in thisway changes in the through flow would be possible, the through flowratio would in each instance remain constant.

The method of the dynamic specific weight compensation has over thestatic method with buoyan y pipe the advantage that it can operate atconsiderably higher pressures above atmospheric pressure whereby roompressure variations will exert a far less influence upon the measuringprecision while the gas jet at the burner nozzle will be ableautomatically to draw in a portion of the combustion air with premixturewhereby a better combustion of gases at a high heating value will beobtained.

With pressure governors, devices as for instance counter Weights orsprings, will compensate the influences exerted upon the controlpressure by the weight of the measuring or control members of thegovernor. This method may be employed for measuring the heating value aswell as for measuring the combustion heat if the waste gas and coolingair are held separate from each other and if the waste gas is cooledback to the ambient temperature.

The specific weight dependent control of the gas pressure by acentrifugal blower may also advantageously be employed with continuouslymeasuring calorimeters employing water as heat carrier, if a centrifugalblower rotating at constant speed is employed for controlling thepressure governor preceding the burner, for automatically holdingconstant the gas flow at the burner nozzle. Varia tions in the specificweight of the gas will be in this way made inelfective and will not anylonger affect the measuring precision. The gas and air streams meteredby the applied pressure and the selectively applicable restrictors orcalibrated nozzles will flow further to the heat exchanger where a smallportion of the air is branched off as combustion air and is conveyedpreferably to a one flame burner as primary or secondary air. While theemployment of a one-flame burner is preferred, it may be added that alsothe employment of multi-flame burners is possible. The by far majorportion of the air will at the combustion chamber exit intermix with thehot waste gases and will be heated up to an extent depending on themagnitude of the heating value. A mixer arranged above the combustionchamber exit and provided with radial deviating blades speeds up theuniform intermixing of waste gases and cooling air. The temperaturedifference between air inlet and waste gas air mixture outlet is takeninto consideration by correspondingly arranged thermoelements, and insaid thermoelernents a thermo tension is produced which is proportionalto the temperature diiference. This thermovoltage is for any desiredreference temperature to be established taken as measurement for theheating value per Nm. gas.

The heating value per Nm. gas can be calculated according to the formulaH LXAt (C +k.G .C kcal./Nm.

kcal. is the measuring unit of the heat quantity 1 kcal.(kilocalorie)=1000 cal. (calories). a

Nm. means normal cubic meter; 1 Nm. gas:l m9 dry gas at a temperature of0 C. and at a pressure of 760 Torr.

Torr. is the customary physical measuring unit for the pressure employedin connection with air pressure measurements by means of a mercurybarometer.

1 Torr.=1 mm. Hg (1 millimeter Hg=l millimeter mercury column).

In this formula H indicates the heating value in kcaL/Nm. gas.

L indicates the air through flow in Nm. referred to l Nm. gas (dry).

The At indicates the temperature difference in degrees .centigradebetween air entrance and waste gas air mixture exit.

c indicates the specific heat of the air in kcal/Nm. C.

o indicates the specific heat of the steam in kcal./kg. C.

G indicates the steam weight in kg/rn. air at the respective conditionand saturation.

k is a factor for converting the steam weight from kg./m.

of humid air into kg/Nm. of dry air.

However, since, as will be evident from the values k and G in Formula 5,the specific heat of the steam saturated air changes with thetemperature and to a minor extent also with the pressure, and since acalorimeter must precisely measure also at various conditions, it isnecessary to measure these effects by an auxiliary device responsive tochanges in temperature and the barometric pressure. It is for thisreason that the thermovoltage produced as starting value in thecalorimeter is conveyed to f a so-called computer. Such computercorrects the thermovoltage and computes the same to a value which isindependent of said influences, which value i by means of an electricalmeasuring instrument indicated or registered as heating value per Nm.gas, or may also be conveyed to a governor as measuring value. Thisconversion or computation may be effected by means of heretofore knowncomputers which operate, for instance, according to the principledescribed in German Patents 459,743 and 640,- 894 for reducing theheating value to a certain normal condition. The devices of said Germanpatents may, when adapted to the calorimeter according to the presentinvention, be employed as computer for said calorimeter. A computerwhich has proved particularly advantageous for use in connection withthe present invention is described in my copending patent applicationSerial No. 151,980 filed of even date herewith, now Patent No.3,153,340.

Referring now to the drawing in detail, the embodiment of a deviceaccording to the present invention comprises a blower 1 which draws airthrough a humidifier 2 where the air is saturated with steam. Morespecifically, the air passes in the direction of the arrow A into thehumidifier 2 where the humidification may be effected, for instance, bywater flowing into the humidifier 2 from above. The water not absorbedby the air is discharged into a discharge pipe 21 which is, in a mannerknown per se, provided with a gooseneck to act a a gas block, whichmeans that the liquid in the gooseneck prevents the passage of air orgas through the discharge pipe. From the discharge pipe 21 the water isfreely discharged into a pipe 22 so that a suction eifect in pipe 22cannot draw liquid out of the gooseneck and thereby destroy the gaslock. Thus, humidified air drawn in by the blower 1 is, at the requiredpressure, conveyed to a pressure control 3 which is controlled by ablower 4 in such a way that the pressure of the air passing throughcontrol 3 will always be equal or proportional to the outlet pressure ofthe blower 4. A branched-oif current of air passes through conduit 5,expanded to atmospheric pressure at a control 10 to the inlet of blower4 and by the latter is compressed to a pressure which is proportional tothe specific weight of the air and higher than the atmospheric pressure.This pressure is conveyed to control 3. Parallel thereto, the

gas passes at the required pressure throng the humidifier 6 which worksaccording to the same principle as humidifier 2, and after beingsaturated with steam, passes to the pressure control 7, which latter,similar to the air pressure control 3, is controlled by the outletpressure of a blower 8 coupled to the blower 4 and which controls thegas pressure to the same or a proportional high pressure. A branched-offcurrent of the gas passes to blower 8 through conduit 9 and the control10 which controls the pressure so as to be equal to atmosphericpressure. The blower 8 compresses the gas to a pressure proportional tothe specific weight of the ga and higher than atmospheric pressure. Thespeed of blowers 4 and 8 is held constant, for instance by the frequencyof the alternating current network, whereas the speed ratio between saidtwo blowers may be held constant by means of a rigid coupling throughthe intervention of a shaft or a transmission. At the thus controlledpressure, the air fiows to the restrictor 11 where it is metered andsimilarly, also, the gas at the burner nozzle 12.

The burner nozzle 12 is'centrally introduced into the calorimeter vesselC which is formed by the cylinder 13 closed at its bottom. In thespecific instance described the heat carrier, air, enters thecalorimeter vessel C at the upper end thereof. The upper portion of thecalorimeter vessel has concentrically arranged therein two pipes 23 and24 which form two annular chambers 25 and 26 which chamber communicatewith each other at the lower ends thereof. The bottom of the chamberconfined by pipe 24 and cylinder 13 is formed by an annular plate 27provided with air apertures 14. A fraction of the air passes throughapertures 14 as combustion air to a burner B which is centrally locatedabove the burner nozzle 12. The by far major portion of the supplied airpasses first downwardly through the annular chamber 25 and then upwardlythrough the annular chamber 26 and above the pipe 24 mixes in mixer 16with the hot waste gases which emanate from the combustion chamberconfined by pipe 24. The mixer 15 will accelerate and complete theintermixture of gas and air by imparting upon the waste gas air mixturea swirl or twist. Corresponding mixers of any known type may be employedfor this purpose. Thereupon, the heated and homogeneous waste gas airmixture passes by the thermoelement soldering points 17 orthermocouples. The comparative soldering points are located in theentering air stream so that in the thermoelements, a thermovoltage willbe produced which corresponds to the temperature differences between thesoldering points 17 and 18. This thermovoltage is computed by thecomputer 19 into a voltage which is proportional to the heating valueper Nmfi, and this last mentioned voltage is, by means of an electroniccompensating amplifier 20, converted by a currentless measurement into aproportional measuring current, which latter flows through a connectingconductor to electric measuring instruments or controls gauged inheating value per Nmfi.

The method according to the present invention is also applicable fordetermining the heating value of dry combustible gases, if the airemployed for the combustion or, as the case may be, as heat carrier, islikewise dry. The method according to the invention will then, whileomitting the saturator for gas and air, work in the described mannerwhile compensating for variations in the specific weight. In thisinstance, the temperature difference measured by the thermoelementscorresponds directly to the heating value of the gases, and theconversion necessary for considering the steam content varying inconformity with pressure and temperature, will be superfluous.

It is, of course, to be understood that the present invention is, by nomeans, limited to the particular arrangement and method described abovebut also comprises any modifications within the scope of the appendedclaims.

What I claim is:

1. A method of continuously and automatically ascertaining the heatingvalue and combustion heat of a combustible gas while employing a gaseousheat carrier in connection therewith, which comprises the steps of:separately branching off a minor portion from each of a main flow ofsaid combustible gas and a main How of said gaseous heat carrier,reducing the pressure of each of said branched ofl portions of saidcombustible gas and said gaseous heat carrier to the same predeterminedlower pressure, thereafter separately centrifugally compressing saidbranched off portions of said combustible gas and said gaseous heatcarrier, respectively, to respective pressures above atmosphericpressure and which pressures are proportional to the specific weight ofsaid combustible gas and said gaseous heat carrier, respectively, andadjusting the main flow of said combustible gas and of said gaseous heatcarrier respectively, to a calorimeter in accordance with the respectivepressures of the compressed branched oil portions of said combustiblegasand said gaseous heat carrier.

2. A method according to claim 1, which includes the step of separatelyhumidifying the main flow of combusti ble gas and the main flow of saidgaseous heat carrier respectively, and prior to the said branching oiftherefrom of the said minor portions thereof.

3. In a device for ascertaining in an automatic and continuous mannerthe heating value and combustion heat of a combustible gas whileemploying a fluid heat carrier in connection therewith: a calorimeterincluding a burner, first main conduit means for conveying a fluid heatcarrier to said calorimeter, first pressure control means interposed insaid first main conduit means, first centrifugal blower means, firstbranch conduit means having a diameter less than that of said first mainconduit means: and branching off from said first main conduit meansahead of said first pressure control means and leading to the suctionside of said first centrifugal blower means, first additional conduitmeans leading from the pressure side of said first centrifugal blowermeans to said first pressure control means, second main conduit meansfor conveying a combustible gas to said calorimeter, second pressurecontrol means interposed in said second main conduit means, secondcentrifugal blower means, second branch conduit means having a diameterless than that of said second main conduit means and branching off fromthe latter and leading to the suction side of said second centrifugalblower means, second additional conduit means leading from the pressureside of said second centrifugal blower means to said second pressurecontrol means, and conduit means leading from said second pressurecontrol means to said burner.

4. An arrangement according to claim 3,. which includes restrictor meansinterposed in said first main conduit means between said first pressurecontrol means and said calorimeter.

5. An arrangement according to claim 3, in which said first and secondbranch conduit means have interposed therein additional pressure controlmeans for adjusting the medium passing therethrough to atmosphericpressure.

6. In a device for ascertaining in an automatic and continuous mannerthe heating value and combustion heat of a combustible gas whileemploying a fluid heat carrier in connection therewith: a calorimetercomprising a cylindrical vessel having a burner located in the centralportion thereof and also comprising passage means for guiding coolingair employed as combusting means and heat carrier, said passage meansdefining a combustion chamber for receiving waste gas and cooling air,first main conduit means for conveying a fluid heat carrier to saidcalorimeter, first pressure control means interposed in said first mainconduit means, first centrifugal blower means, first branch conduitmeans having a diameter less than that of said first main conduit meansand branching off from said first main conduit means ahead of said firstpressure control means and leading to the suction side of said firstcentrifugal blower means, first additional conduit means leading fromthe pressure side of said first centrifugal blower means to said firstpressure control means, second main conduit means for conveying acombustible gas to said calorimeter, second pressure control meansinterposed in said second main conduit means, second centrifugal blowermeans, second branch conduit means having a diameter less than that ofsaid second main conduit means and branching off from the latterand'leading to the suction side of said second centrifugal blower means,second additional conduit means leading from the pressure side of saidsecond centrifugal blower means to said second pressure control means,

conduit means leading from said second pressure control means to saidburner, and mixer means arranged above said combustion chamber forintensively intermixing said waste gas and said cooling air in saidcombustion chamber.

7. An arrangement according to claim 3, in which said first main conduitmeans and said second main conduit means have respectively interposedtherein first and second humidifier means respectively preceding saidfirst and second branch conduit means when looking in the di-Relferences Cited by the Examiner UNITED STATES PATENTS 1,625,277 4/27Packard 73-190 1,923,331 8/33 Smith 73l90 X FOREIGN PATENTS 503,164 4/39Great Britain,

RICHARD C. QUEISSER, Primary Examiner.

JOHN P. BEAUCHAMP, Examiner.

1. A METHOD OF CONTINUOUSLY AND AUTOMATICALLY ASCERTAINING THE HEATINGVALUE AND COMBUSTION HEAT OF A COMBUSTIBLE GAS WHILE EMPLOYING A GASEOUSHEAT CARRIER IN CONNECTION THEREWITH, WHICH COMPRISES THE STEPS OF:SEPARATELY BRANCHING OFF A MINOR PORTION FROM EACH OF A MAIN FLOW OFSAID COMBUSTIBLE GAS AND A MAIN FLOW OF SAID GASEOUS HEAT CARRIER,REDUCING THE PRESSURE OF EACH OF SAID BRANCHED OFF PORTIONS OF SAIDCOMBUSTIBLE GAS AND SAID GASEOUS HEAT CARRIER TO THE SAME PREDETERMINEDLOWER PRESSURE, THEREAFTER SEPARATELY CENTRIFUGALLY COMPRESSING SAIDBRANCHED OFF PORTIONS OF SAID COMBUSTIBLE GAS AND SAID GASEOUS HEATCARRIER, RESPECTIVELY, TO RESPECTIVELY PRESSURES ABOVE ATMOSPHERICPRESSURE AND WHICH PRESSURES ARE PROPORTIONAL TO THE SPECIFIC WEIGHT OFSAID COMBUSTIBLE GAS AND SAID GASEOUS HEAT CARRIER, RESPECTIVELY, ANDADJUSTING THE MAIN FLOW OF SAID COMBUSTIBLE GAS AND OF SAID GASEOUS HEATCARRIER RESPECTIVELY, TO A CALORIMETER IN AC-